Illustrated herein, in various exemplary embodiments, is a process for forming toner compositions for use in electrophotographic and xerographic printing processes, and the toners formed thereby. In particular, the disclosure relates to a process for forming a toner particle by combining a base toner composition, dry pigment and a dispersing agent in a single processing step. The process is particularly directed to forming toner particles for xerographic printing processes and will be described with particular reference thereto. It will be appreciated that the process may be amenable to forming other pigmented items.
In an electrophotographic application such as xerography, a charge retentive surface (i.e., photoconductor, photoreceptor, or imaging surface) is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as “toner.” Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface.
The aforementioned process is known, and useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be image-wise discharged in a variety of ways. Ion projection devices where a charge is image-wise deposited on a charge retentive substrate operate similarly.
Electrophotographic imaging members are commonly multilayered photoreceptors that, in a negative charging system, include a substrate support, an optional electrically conductive layer, an optional charge blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer, and an optional overcoating layer. The photoreceptor or imaging members can take several forms, including flexible belts, rigid drums, and the like.
Toners employed in color electrostatographic or xerographic printing processes include pigments to impart color to the toner particles and compositions. Color toners are generally prepared using pigment concentrates and dispersions. Dry pigment materials may be directly used to form color toner particles or compositions.
Pigment dispersions are often utilized in the form of flushed color dispersions, which are also known and referred to as pigment flushes or flushed pigments. Flushed pigments are prepared by a process known as “flushing.” Flushing involves removing water from a pigment presscake with a vehicle that is compatible with the final toner binder resin. In the flushing process, pigment presscake is loaded into the flusher and a resin or oil is added to yield a high viscosity paste. The paste is then mixed until a dispersion is formed. The resin displaces the water surrounding the pigment particles, which separates into a clear layer that is poured or decanted off. It may take several cycles of the above steps to fully remove the water and replace it with the resin. The final traces of water may be removed by heat and/or vacuum. Following their preparation, the flushed pigments are added to the melt blending step of the toner preparation process.
Flush pigments offer several advantages over dry pigments. Mixing dry pigments with other toner ingredients often results in non-uniform dispersions, which may result in toners with poor color quality. Uniform dispersion of a colorant, such as a pigment, is important to obtain a large color gamut, minimize the amount of toner laid down on a page, and to achieve reproducible color, electrostatic, and other physical properties. Additionally, uniform dispersion is important in optimizing the production costs for obtaining the toner. Further, dry pigments are often too difficult to handle and meter.
One of the drawbacks to the use of flush pigments is an increase in the cost to produce toners using such pigments. Namely, the processing steps to obtain flushed pigments add to the costs of producing such pigments and, therefore, add to the cost of producing toners with flush pigments. Consequently, there is a need to provide a process for forming a toner composition that can utilize dry pigments, and eliminate the flushing step or process. It is also desirable to provide a process, utilizing dry pigments free from any flushing process, which provides a toner composition that exhibits satisfactory dispersion and provides colors and other properties comparable to toners prepared from flush pigments.
Additionally, it is desirable to provide a xerographic printing process that provides a high print quality such that it may be a suitable alternative to offset lithography. Generally, offset lithography demands a level of print quality much higher than is available with typical xerographic machines and processes. Additionally, offset lithography is more cost effective for long print runs. Xerography and the digital imaging processes of certain xerographic products allows customization of each print, such as an address, or special information for regional distribution, which is not practical with offset lithography. It is therefore desirable to provide a xerographic printing process that can produce prints of sufficient quality such that it may be a suitable, low cost, alternative to offset lithography, and particularly when the desired number of prints is below a certain number corresponding to the break even point for lengthy pre-press activities.
Therefore, it is desirable to provide toners formed from dry pigments that exhibit satisfactory dispersion and provide colors and other properties comparable to toners prepared from flush pigments. Along these lines, it is desirable to provide a process for preparing toners using dry pigments.